So I've been using catalyst drivers forever but I wanted to use the open source radeon driver (xf86-ati) and suddenly dota 2 won't launch. Steam says it is running, and the process exists but it doesn't appear to be running. If I launch dota2 from /.steam/steam/steamapps/common/dota\ 2\ beta/game/bin/linuxsteamrt64/ then I can see the following error:

failed to dlopen "" cannot open shared object file: No such file or directory
Not sure why this works fine with catalyst. Anyway with my googlefu I got around this by doing
ln -s /usr/lib/ /.steam/steam/steamapps/common/dota\ 2\ beta/game/bin/linuxsteamrt64/
Now the game launches from the CLI! still doesn't work from steam though...
Anyway I hope this helps the few manjaro users out there. I personally think the game looks smoother with the open source driver.
Maybe some smart valve employee with too much free time can figure out a way to bundle or detect the host OS libudev better.